It is well known to separate particles, such as dirt and dust particles, from a fluid flow using a cyclonic separator. Known cyclonic separators are used in vacuum cleaners, for example, and have been known to comprise a low efficiency cyclone for separating fluff and relatively large particles, and a high efficiency cyclone located downstream of the low efficiency cyclone for separating the fine particles which remain entrained within the airflow. It is also known to provide an upstream cyclonic separator in combination with a plurality of smaller, downstream cyclone bodies, the downstream cyclone bodies being arranged in parallel with one another. An arrangement of this type is shown and described in U.S. Pat. No. 3,425,192.
In vacuum cleaner applications, particularly in domestic vacuum cleaner applications, it is desirable for the appliance to be made as compact as possible without compromising the performance of the appliance. It is also desirable for the efficiency and performance of the separation apparatus contained within the appliance to be as high as possible (i.e. to separate as high a proportion as possible of very fine dust particles from the airflow). In addition, it is desirable for vacuum cleaners to be as energy efficient as possible, without compromising cleaning performance. This is particularly the case for battery powered vacuum cleaners, such as handheld vacuum cleaners, and also battery powered cylinder and upright vacuum cleaners. A typical method of increasing the separation performance and efficiency of a cyclonic separator is to decrease the size of the downstream cyclone bodies. Making the cyclone bodies smaller increases the centrifugal forces within the cyclone body, and therefore improving separation of the dust and dirt from the airflow. However, decreasing the size cyclone bodies also reduces the volume of air that each cyclone body can handle. To overcome this, additional cyclone bodies are provided to maintain the desired airflow, and to stop a bottleneck being created at the downstream cyclone stage. For example, the cyclonic separator on a Dyson DC59 handheld vacuum cleaner has a secondary cyclone stage that contains fifteen small cyclone bodies in parallel in order to provide the desired separation performance. Indeed, some cyclonic separators are known to contain up to fifty-four small cyclone bodies in parallel, such as on the Dyson DC54 cylinder vacuum cleaner. However, increasing the number of smaller cyclone bodies will also result in an increase in size for the separator, and therefore the overall machine. Furthermore, the energy required to pass airflow through multiple small cyclone bodies is significant, and in the case of battery powered vacuum cleaners this can have a detrimental effect on battery life.